Background: Addition of amino acids to culture media improves the rate of blastocyst development. But, amino acid metabolism releases ammonia which has deleterious effects on the embryo development. Finding this threshold level above which its deleterious effect starts can help make appropriate changes in media or embryo environment.

Materials and methods: It is a prospective cohort study carried out on 86 frozen–thawed mouse embryos which were randomly divided into 3 groups and were exposed to varying concentrations of ammonium chloride (control KSOM, KSOM with 38 µM ammonium chloride and KSOM with 75 µM ammonium chloride). These embryos were cultured individually in embryoscope dishes till 5 days during which morphokinetic, morphometric and morphological parameters were noted and compared within all 3 groups of the embryos. On 5th day apoptosis in blastocysts of each group was studied by staining the blastocysts with TUNEL stain with counter stain of DAPI.  Total number of cells and percentage of apoptosis in the blastocysts developed in each group were noted and compared within all 3 groups.

Results : Rate of pronuleus fading and time taken to reach 2 cell stage was significantly less in the embryos cultured in 38 µM and 75 µM ammonium chloride. Significant decrease in percentage of apoptosis and increase in total cell count was observed in the blastocysts obtained from the embryos cultured in 38 µM and 75 µM ammonium chloride in comparison to the blastocysts obtained from the embryos cultured in control group.

Conclusion: Ammonium chloride in lower concentration may have beneficial effect on the embryo development.